Controlling a laser used with an optical disk apparatus

Abstract

During playback of data from a recording medium, a light source emitting a light beam incident on the recording medium is driven by a first drive circuit. During this time, a first control circuit produces a control signal to the first driving circuit and controls the first drive circuit such that a power of the light beam is kept constant. During recording of data, on the other hand, a second drive circuit supplies a drive current in superimposition on a drive current from the first drive circuit with a timing corresponding to the recording data. During this time, the control of first drive circuit by the first control circuit is inhibited. However, the control signal immediately before the inhibition is held, and hence the light source is continually driven by the first drive circuit. Thus only a single reference level is necessary for the power control, thus permitting simplification of the construction and cost reduction.

What is claimed is: 
     
       1. An automatic power controlling apparatus, comprising: first means for driving a light source which emits a light beam at the time of playing back data from a recording medium and also at the time of recording data thereon;   second means for driving said light source according to said recording data at the time of recording;   means for generating a control signal to control said first drive means corresponding to a difference between a power of said light beam emitted from said light source and a first reference level so that said power of said light beam is kept constant; and   means for inhibiting said control of said first drive means by said control means at the time of recording and also for causing said first drive means to supply a constant current to said light source.   
     
     
       2. An automatic power controlling apparatus according to claim 1, wherein said light source comprises a semiconductor laser, and said light beam comprises a laser beam, said apparatus further comprising a photo detector for detecting at least a part of said laser beam emitted from said semiconductor laser and generating a signal in compliance with said power of said laser beam.   
     
     
       3. An automatic power controlling apparatus according to claim 2, wherein said control means comprises: means for generating said first reference level; and   means for comparing said power of said laser beam and said first reference level.   
     
     
       4. An automatic power controlling apparatus according to claim 3, wherein said first reference level generating means comprises a zener diode and said comparing means comprises at least one resistor for converting a current outputted from said photo detector into a voltage and at least one transistor for comparing said first reference level with said voltage converted by said resistor.   
     
     
       5. An automatic power controlling apparatus according to claim 1, wherein said inhibiting means comprises: means for controlling a transmission of said control signal from said control means into said first drive means; and   means for holding said control signal.   
     
     
       6. An automatic power controlling apparatus according to claim 5, wherein said holding means comprises a capacitor and said switching means transmits said control signal to said capacitor at the time of playback, and inhibits said transmission of said control signal to said capacitor and has a voltage charged on said capacitor to be supplied to said first drive means at the time of recording.   
     
     
       7. An automatic power controlling apparatus according to claim 1, wherein said second drive means comprises a current mirror circuit.   
     
     
       8. An automatic power controlling apparatus according to claim 1, wherein said apparatus further comprises means for detecting abnormalities of said light source.   
     
     
       9. An automatic power controlling apparatus according to claim 8, wherein said detecting means comprises: means for detecting a current driving said light source at the time of playback and converting said current into a voltage; and   second means for comparing said voltage with a second reference level.   
     
     
       10. An automatic power controlling apparatus according to claim 1, wherein said recording medium is a CAV type disk, said apparatus further comprising: means for generating a second control signal in compliance with a recording position in a radial direction of said disk; and   means for controlling said second drive means according to said second control signal.   
     
     
       11. An automatic power controlling apparatus according to claim 1, wherein said second drive means includes a switching means for switching in accordance with said recording data.